* kame/sys/netinet6/nd6_rtr.c (in6_{ifadd, ifdel}): ifa_refcnt
clarifications:
- do not IFAREF in in6_ifadd() (except on nbsd)
- do not duplicate IFAFREE in in6_ifdel() (except on nbsd)
without these changes, a manually configured ifaddr would be freed
two times when its lifetime expired. Although such a situation
would be rare, all *BSD (except NetBSD) users (who use versions
after Jan 2, 2001) are recommended to apply this fix.

- do not IFAREF in in6_ifadd() (except on nbsd)
- do not duplicate IFAFREE in in6_ifdel() (except on nbsd)
without this, manually configured ifaddr will be freed two times when its
lifetime expires.
(fortunately, such a situation would be rare, but this change is still very
important. be sure to update)

…it is
successful.
FreeBSD PR 24248. notified by ume.
XXX it is hard to understand why it is made this way.
under 4.4BSD networking code rule, once a function is passed a mbuf *,
it always get freed by the function. at least the behavior violates the
(implicit) coding rule.